This invention relates to a high frequency ferroresonant power supply for a deflection and high voltage circuit.
In deflection and high voltage power supplies for television receivers, the B+ supply voltage for the deflection circuitry and the high voltage ultor accelerating potential typically are derived in two different manners. The B+ voltage is derived from the AC line mains which is rectified and filtered; whereas the ultor accelerating potential is derived from rectified flyback pules obtained from a horizontal output or flyback transformer. With such an arrangement, two relatively independent and costly power supplies must be used.
To regulate the high voltage, either the high voltage itself is regulated directly or the B+ voltage is regulated typically through relatively complex electronic series switching, or shunt regulators. Such circuits are relatively costly and subject to failures which require additional protective circuitry to disable the television receiver under abnormal increases in high voltage.
Many television receivers include circuitry to maintain a constant raster width with varying ultor beam current. This can be accomplished by altering the B+ raster voltage so that it tracks the changing ultor voltage in such a way that the raster width and thus the picture size remains constant with changing ultor voltage. Typically, the B+ voltage change is accomplished by inclusion of a series resistor conductively coupled to the flyback transformer primary winding or by use of additional B+ regulator control circuitry which senses beam current variations and correspondingly changes the B+ voltage. In the former approach, power may be unnecessarily dissipated in the series resistor, while in the latter approach additional circuit complexity and cost may be incurred.
Some B+ regulators employ a 60 Hz AC line mains regulating transformer, such as a 60 Hz ferroresonant transformer, to provide a regulated B+ voltage. Because operation is at the low frequency of 60 Hz, a relatively large and heavy transformer must be used. Furthermore, the high voltage is then independently supplied by means of a relatively large flyback transformer designed to accommodate relatively large power flows.
Other television receiver regulator circuits discussed in the prior art, regulate the high voltage by providing a flyback transformer which itself is operated in the ferroresonant mode. Flyback pulses are coupled to the flyback primary winding. The ultor high voltage winding is then tuned to the desired frequency. Because the B+ supply is derived from a separate source such as the AC line mains supply, a separate regulator circuit must be provided if the B+ voltage is also to be regulated. If the B+ voltage is unregulated, other circuitry may be required to maintain a constant raster width.
In many typical flyback derived high voltage circuits, the high voltage provides a peak voltage substantially less than the required ultor potential in order to reduce the number of turns required of the high voltage winding. A high voltage multiplier then steps up the voltage to the required level. Since the design of many voltage multipliers requires that both polarities of the AC voltage be used, it is desirable for the multiplier to be driven by an AC voltage with positive and negative polarities close to being equal. If one polarity is much smaller than the other, the capacitors and diodes active during this polarity contribute very little voltage step up. This is the situation when using the flyback pulse as a source for a voltage multiplier circuit. A sextupler multiplier using six diodes and six capacitors is required to obtain a three times multiplication when a low duty cycle flyback pulse is applied to a voltage multiplier.